The broad, long-range objectives of this Program Project Grant are to inquire and communicate new and fundamental knowledge of the chemical composition, molecular structure, molecular biology, tissue organization and physiological functions of the cells, specific components and compartment of cells and the individual components of the organic and inorganic mineral components of mineralized connective tissues, with particular reference to bone and tooth and to explore the structural and chemical interactions and the relationships between them. A major effort will be made and directed to studies of the molecular steps comprising specific tissue component calcification and to the features specific to these tissues and to those components which distinguish them from other unmineralized connective tissues. We feel that these specific tissue components and the features which distinguish the calcification of individual cellular and extracellular components of the mineralized tissues are important since these specific characteristics are likely to play a critical role in defining their biological function. Our research projects cover all levels of the anatomical hierarchy starting with ultrastructural investigations on the organization of the mineral and organic component including high resolution transmission electron microscopy and electron probe microanalysis, electron diffraction, the new techniques of examining tissues by electron optics using the frozen hydrated and environmental stages, and high resolution electron microscopic immunocytochemical techniques using antibodies to the major non-collagenous proteins thought to be intimately and critically involved in tissue calcification. The answers to these and other important questions will be sought by integrating data from a wide variety of scientific disciplines and techniques, which include in addition to the ultrastructural analyses above, the full range of biochemical, physical chemistry and molecular biology. We feel that such an indepth and multifaceted concentrated research effort centered about the basic biology and pathophysiology of the skeletal system at all levels of the anatomical hierarchy, i.e., molecular, cellular, tissue, organ and whole organism levels will provide a more complete understanding of tissue calcification and calcified tissues, and provide additional information for a more rational basis which can be used for the diagnosis, treatment, and prevention of diseases of the skeletal system which now disable a large part of the population.